Exercise has been found to have positive effects on mental health in both clinical and nonclinical populations. Research suggests that exercise is associated with decreases in depression and anxiety, tension reduction, increased feelings of well-being, and improved self-concept and confidence. Unfortunately, statistics show that many people do not exercise regularly, and that many of those who begin exercise programs drop out within the first few months. At present, it is extremely difficult to design intervention to promote exercise initiation and exercise adherence because of the lack of a good theory of exercise behavior. The proposed research represents the first phase of a larger research project, the goal of which is to understand exercise behavior and to develop interventions to promote exercise initiation and exercise adherence. Subjective expected utility theory analyses of (1) exercise initiation among male and female college students and (2) exercise adherence among coeds participating in an aerobic dance class will be conducted. The research will examine the usefulness of behavioral decision theory as a theoretical framework for exercise initiation and exercise adherence. In addition, the research will generate information that will be used in future research as a basis for designing interventions to promote exercise initiation and exercise adherence. Finally, the reseach will examine the relationship between previous exercise experience and beliefs about the consequences of exercise adherence. The study of exercise adherence also serves as a first step toward the development of a general model of adherence behavior.